In this post we recap the week’s most interesting influxQL query examples, InfluxDB and TICK-stack related issues, workarounds, how-tos and Q&A from GitHub, IRC and the InfluxDB Google Group that you might have missed.
Understanding unexpected fill() behavior
Q: I’m using `fill(0)` in my query but it doesn’t return any results. Is this the expected behavior?
A: If none of your data fall within your query’s time range, your query will return no results – even if your query includes `fill()`. This is how `fill()` currently works but there is an open issue to change that behavior.
Write one data point:
> INSERT invisible person=7 1467842220000000000 > SELECT * FROM "invisible" name: invisible --------------- time person 2016-07-06T21:57:00Z 7
Use `fill(0)` and query a time range that includes the point:
> SELECT mean("person") FROM "invisible" WHERE time >= '2016-07-06T21:57:00Z' AND time <= '2016-07-06T21:59:00Z' GROUP BY time(1m) fill(0) name: invisible --------------- time mean 2016-07-06T21:57:00Z 7 2016-07-06T21:58:00Z 0 2016-07-06T21:59:00Z 0
Use `fill(0)` and query a time range that doesn’t include the point:
> SELECT mean("person") FROM "invisible" WHERE time >= '2016-07-06T21:58:00Z' AND time <= '2016-07-06T21:59:00Z' GROUP BY time(1m) fill(0)
Querying for the latest point in a measurement
Q: I’m trying to find the last point in my measurement. I’ve included the query that I use to do that, but I’m wondering – is there a better way to do this?
> SELECT "dance_id" FROM "ballroom" ORDER BY time DESC LIMIT 1 name: ballroom -------------- time dance_id 2016-07-06T20:26:10Z 103
A: Yes! There’s an InfluxQL function (`LAST()`) that returns the last point in a measurement:
> SELECT last("dance_id") FROM "ballroom" name: ballroom -------------- time last 2016-07-06T20:26:10Z 103
InfluxDB Tech Tips Video
Check out the video below from the June 2016 InfluxDB Meetup for tips on series cardinality, `INTO` queries, and more.
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